Known linear drives of the kind set forth above frequently involve travel measurement with roller sensors which start from a zero position. In the event of the power being switched off, for example as a consequence of the linear drive not being in use for a prolonged period of time, then for renewed travel measurement so-called zeroing is required to establish a fresh zero position which however is independent of the previous zero position.
That disadvantage is overcome by rotary-potentiometric travel measurement, in which case a rotary potentiometer, connected to the linear drive by way of a step-up transmission arrangement or directly, measures the stroke involved, by way of the number of revolutions of the rotary spindle. That measurement procedure is relatively complicated and expensive and quite inaccurate for example due to screwthread play which occurs.
Therefore the object of the invention is to provide a linear drive of the kind set forth in the opening part of this specification, having travel measurement which is not complicated and expensive, which operates in a reproducibly accurate fashion and which even after power shut-down does not require renewed zeroing for travel measurement.